LED fluorescent lamps, component selection and packaging are key

The goal of straight tube type LED lamps is to replace straight tube fluorescent lamps used in offices and the like. On December 24, 2010, Matsushita began supplying the first straight-tube type LED lamp system that supports the Japanese lamp industry association specification "JEL801:2010". The LED lamp system supports the just-standardized L-shaped lamp socket, which is clearly defined by the original straight tube type LED lamp that previously used the G13 fluorescent lamp socket (Fig. 1). The product was very popular as soon as it was launched, and it was alleged that “the order was more than expected” (the company). In January 2011, Toshiba Lighting Technology also plans to launch products that support this specification.
According to Matsushita Electric Works, the lamp system that meets the JEL801:2010 specifications, the current goal is to meet the "LED" requirements of the fluorescent system that has entered the replacement period. This straight tube LED system reduces power consumption by approximately 42% compared to fluorescent systems. However, to meet the needs of the replacement, it is estimated that not only low power consumption, but also the performance of lighting from under the lamp to the wall is not inferior. At the time of product delivery, Panasonic disclosed development points for achieving good lighting performance.

New and old lighting fixtures are lit at the same time. Fluorescent light on the left and LED light on the right
Decentralized configuration of LED chips  
The original straight tube type LED lamp always has many problems such as a plurality of LED light-emitting points being granular, light glare, color spots and chromatic aberrations, and light rays directed to the side direction (wall surface, etc.) are weak and cannot illuminate the entire room. This is also the reason why the user feels uncomfortable when replacing the fluorescent lamp with the LED lamp.
In order to solve these problems together, a long strip LED unit was used this time. On the ceramic substrate, a blue LED chip was mounted equidistantly upward and coated with a silicone resin mixed with a phosphor (Fig. 2). Light emitted from the surface and side directions of the blue LED chip causes the phosphor to emit light, thereby causing the entire LED unit to emit light. The use of a diffusion film between the glass tubes eliminates the graininess of the light-emitting points. The light loss caused by the diffusion film is only 2%.

Previously, because the packages of multiple LED chips were juxtaposed, there was no light-emitting between the packages. In addition, coating with a resin tube having a light diffusing function also caused a light loss of 10%.

Although the number of blue LED chips is not disclosed, a plurality of small-sized chips having a common shape are mounted 1) . The glare of the LED chip is finely dispersed, making the glare less dazzling. According to Matsushita Lighting Co., Ltd., which is responsible for the development of LED units, LED modules with multiple small chips mounted and packaged like this have been used in the development of LED bulbs .

Note 1) The general-purpose small blue LED chip has a single-sided size of 200μm to 300μm.

Figure 1: Lighting system supporting L-shaped lamp socket
The direct-tube type LED lamp system that Panasonic Electric Works has started to market meets the specifications of the Japan Light Bulb Industry Association "JEL801:2010". The lamp is composed of a straight tube type LED lamp, a lamp socket, a power module, and a casing (a). Improvements such as fall prevention (b) have also been made.

Figure 2: Mounting the LED on a ceramic substrate
The straight tube type LED lamp is internally provided with a plurality of elongated LED units (a) having a length of 140 mm. The LED unit is provided with a plurality of blue LED chips mounted on a ceramic substrate, and is surrounded by a silicone resin (phosphor layer in the figure) mixed with a green and red phosphor material. It is said that glare is reduced and the graininess of light is less than that of the original mounting method. In addition, the length of the LED unit is an estimated value. (Photo: (b) Based on the data of Matsushita Electric Works)
"Natural" comes from shapes and phosphors
The silicone resin mixed with the phosphor is a semi-cylindrical shape extending in the longitudinal direction. It is intended to reduce stains and chromatic aberrations. The distance of the light passing through the phosphor from the blue LED chip becomes less dependent on the position of the LED chip (Fig. 3). In addition, the LED unit not only has a surface, but also emits light from the side, so that the light is more easily illuminated to the wall after installation.

Figure 3: Covered with a semi-cylindrical resin to eliminate stains
The silicone resin covers the blue LED chip in a shape similar to a semi-cylindrical shape. When the light emitted from the blue LED chip is emitted to the outside, the optical path length through the resin is almost the same, so that the generation of the color unevenness can be suppressed. (The picture is based on information from Matsushita Electric Works)

The phosphor uses a green phosphor and a red phosphor. The average color rendering index (Ra) is 84, which satisfies the JEL801:2010 specification for Ra to reach 80 or more. The color rendering of red (R9) not included in the Ra evaluation is guaranteed to be 30. Its color rendering has reached the same level as current mainstream fluorescent lamps.

The idea of ​​developing with the fluorescent lamp standard is also reflected in the system's power circuit and component selection. For example, a power supply circuit (AC-DC converter), although supplying a constant current of 350 mA to an LED lamp, actually has some high-frequency components in the current. Panasonic Electric Works has improved the power supply circuit in order to achieve the same level of flicker as the current mainstream Hf fluorescent lamp. The switching frequency is selected from 50 kHz to 60 kHz.

In terms of component selection, the outer casing portion of the system and the portion housing the power module can be used in common with systems that use fluorescent lamps. This is to suppress the cost of the parts by generalizing the parts.

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